• R
    x86/smp: Don't ever patch back to UP if we unplug cpus · 816afe4f
    Rusty Russell 提交于
    We still patch SMP instructions to UP variants if we boot with a
    single CPU, but not at any other time.  In particular, not if we
    unplug CPUs to return to a single cpu.
    
    Paul McKenney points out:
    
     mean offline overhead is 6251/48=130.2 milliseconds.
    
     If I remove the alternatives_smp_switch() from the offline
     path [...] the mean offline overhead is 550/42=13.1 milliseconds
    
    Basically, we're never going to get those 120ms back, and the
    code is pretty messy.
    
    We get rid of:
    
     1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the
        documentation is wrong. It's now the default.
    
     2) The skip_smp_alternatives flag used by suspend.
    
     3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end()
        which were only used to set this one flag.
    Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
    Cc: Paul McKenney <paul.mckenney@us.ibm.com>
    Cc: Suresh Siddha <suresh.b.siddha@intel.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/87vcgwwive.fsf@rustcorp.com.auSigned-off-by: NIngo Molnar <mingo@kernel.org>
    816afe4f
alternative.h 8.3 KB